Currently (r48481), the Copy menu item in the Edit menu does not seem to copy anything from the DOM tree in the Inspector. It could be useful to be able to copy HTML code from the DOM tree, for instance in the case of a node that has been created or modified through JavaScript.
This bug probably overlaps bug 20663 in scope and purpose: https://bugs.webkit.org/show_bug.cgi?id=20663
Copy should work, there is a bug with copy from the context menu but Command-C and the view menu item work for me on Mac.
Yes, it works for me, too in r51669 using Cmd-C.